CB550 acceleration issues in 3rd gear

akabek

akabek

New Member
I have a 1975 CB550 with about 200KM on it this season without issue. About a week ago while working on carb jetting I noticed while accelerating the bike would have multiple hesitations in a row until red line. Some info on my bike:
Dynoman DP592 SV pistons 10.5:1
Pamco Ultimate ignition
Ported & decked head, valve job
CB650 cam
MAC 4-1 header with Cone Engineering muffler
Keihin CR26 carbs with K&N pods.

This is my current jetting: Main 105, pilot 65, needle YY7 5th position, Air jet 220 and mix screw 1 turn out. The is the best pull I have experienced to date with jetting but while cruising below 5000 RPM I cannot go WOT without it bogging.

Yesterday I installed a fresh set of Denso plugs and the hesitation is still there. I decide to take a video and while reviewing it I discovered this was only happening in 3rd gear. I checked my fuel lines and petcock and no debris. I have in line fuel filters which I am going to remove today. I will have to check if this also occurs when the engine is cold but the hesitation also happens when slowly accelerating.

I strapped a GoPro to a helmet and took some video. The sound has a lot of wind in it but you can hear the hesitation I experience. If you listen to the gear changes you will see if only happens in 3rd gear.

To avoid watching the entire video here is where the hesitations happen
1:48
3:12
5:50
6:32
8:18
8:41
9:39
10:07
11:35

https://www.youtube.com/watch?v=qhLJc4MBov0

Any suggestions would be appreciated.
 
Do plug chop at that speed in that gear and see what your mixture looks like...
 
frogman said:
Do plug chop at that speed in that gear and see what your mixture looks like...
Click to expand...

Since this problem showed up a week ago I have left the jetting and road the bike with open stacks, stacks with filters and pods. In that video I was running pods. In all cases every gear is fine except 3rd. Wouldn't a rich or lean jetting effect all gears not just 3rd?
 
Finnally got the vid to load had to get on a PC that works.

How does it act just easing into the throttle in all gears? A couple of those times it almost sounded like it was running out of gas. Might check to make sure you are not starving cabs, full throttle runs up to and through 3rd might drain the bowls. Can you back off the throttle a second or two and then get back on it and its fine? What RPM does it do it at? Does giving it just a hair of choke stop it or make it worse? Stupid thought, is the choke staying OPEN when you are riding?

Check timing advance, make sure it is doing what it is supposed to do and not over advancing. Make sure the pickups on the pamco are not getting loose or possibly look for vibration at that RPM.

My 550 did/does that kind of crap but it has not gone through rejetting since I'm not done with it yet. It needs about half choke to run with any kind of decency if I just take it around the block. Haven't ridden it in months so god knows what it does now.

If it only happens in 3rd then you may have internal issues what I couldn't tell you. I would really try hard to figure out if it happens in all, as that would indicate at least a carb or timing issue.
 
frogman said:
Finnally got the vid to load had to get on a PC that works.

How does it act just easing into the throttle in all gears? A couple of those times it almost sounded like it was running out of gas. Might check to make sure you are not starving cabs, full throttle runs up to and through 3rd might drain the bowls. Can you back off the throttle a second or two and then get back on it and its fine? What RPM does it do it at? Does giving it just a hair of choke stop it or make it worse? Stupid thought, is the choke staying OPEN when you are riding?

Check timing advance, make sure it is doing what it is supposed to do and not over advancing. Make sure the pickups on the pamco are not getting loose or possibly look for vibration at that RPM.

My 550 did/does that kind of crap but it has not gone through rejetting since I'm not done with it yet. It needs about half choke to run with any kind of decency if I just take it around the block. Haven't ridden it in months so god knows what it does now.

If it only happens in 3rd then you may have internal issues what I couldn't tell you. I would really try hard to figure out if it happens in all, as that would indicate at least a carb or timing issue.
Click to expand...

The bike runs great in all gears except 3rd. It only does the hesitation when accelerating, putting a load, in 3rd gear. If I had jetting issues or ignition issues I should see problems in other gears.
 
barnett468 said:
.
i would try 2 sizes smaller on the mains and if that doesn't fix it i would try 2 sizes bigger.
Click to expand...

Carb jetting effects all gears. My issue is only in 3rd gear....
 
akabek said:
Carb jetting effects all gears. My issue is only in 3rd gear....
Click to expand...

actually, i have done this for nearly 40 years and have worked on the fastest bikes in the world so i know exactly what carb jetting does . . i also watched your video.

things like this can be hard to figure out especially from behind a computer screen so i would simply take my suggestion instead of wondering why it seems to only do it in 3rd gear because it certainly isn't going to fix itself.

you will not know why it only seems to do it in third gear until after you find the cause, but my guess is that it would do something similar in other gears under the right condition.

i would also check the float level.

as part of your testing procedure, i would also go at a steady 2000 rpm in second for a few seconds then open the throttle all the way . . i would then do the same thing in third.

it might also help to have a photo of the spark plugs.
.
 
if it only recently became an issue while messing with jetting, it's most likely jetting....otherwise, check/adjust float height and carb sync
 
This issue popped up about two weeks ago. I am working on the jetting but I am using a jetting setup that did not cause this problem in the past.

Last Saturday I rode to a buddies place which is about a 35 minute ride one way. The issue seems to be getting worse. Before the bike would cruise in third gear and while cruising or slowly accelerating it feels like it is slipping similar to a slipping clutch. When you accelerate quickly in 3rd gear you will reach red line but with 5-6 quick jolts/hesitations as seen in the video. My buddy initially thought is was the clutch but after a couple of rides he also found the issue baffling.

Last weekend I checked my float levels, replaced the fuel lines and cleaned out my gas tank adding fresh fuel. I have no issue making more jetting adjustments as that is much easier than splitting the cases.

I will pull out my 105 mains and replace them with 100s. I will also try the 2000RPM test to see how it goes.

I just have a gut feeling I may have a bent shift fork or a dog is worn....
 
.
ok well unfortunately, a bad trans that goes in and out is much harder to determine from a video because we mainly just hear the revs being irregular but it would not be the clutch because the clutch always has a similar load on it under acceleration which would definitely narrow it down to a bad gear possibly being the culprit.

if you are absolutely positive that it only does it in 3rd gear, then i think the evidence is overwhelmingly pointing to a bad gear
 
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i just listened to your video again and it definitely sounds to me like it is breaking up at max rpm in every gear you wind out in.
 
I went ahead and dropped my mains down from 105 to 100s. This issue still persists but only in 3rd gear. I tried cruising and slightly accelerating in 3rd gear and it feels like is slips out and back into gear. That is the best way I can explain it. There is no doubt my jetting needs adjustment but this issue feels like the transmission. I think will just pull the engine.

I have already rebuilt the top end and I read you can flip the engine on it head to split the cases and work on the transmission. This would be easier than removing the top end but will this be a bigger pain to do it this way?
 
I fixed this issue last summer but I forgot to post my findings.

What I found was that in the gear shift linkages behind the right engine cover the stopper arm that holds the drum, gearshift assembly in place was bent outward. This was allowing the shaft to slide left and right and not hold 3rd gear in place. In the attached picture the yellow mark is the stopper linkage and the red mark is pointing to the end of the shaft. Bending the stopper back into position held the shaft in place so the assembly would stay in 3rd gear.
 

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